What can you expect to see in a telescope?

Do you want to read the home port of an ocean-going freighter as it pulls into harbor a half-mile away, or spy on a robin feeding her chicks in the tree in your backyard – with only an occasional look at the stars? If this kind of observing fascinates you, then binoculars or a simple spotting scope may fill the bill.

Do you want to look up in the fall and winter and experience the full sweep of the 3° wide Andromeda Galaxy, or marvel at the face-on spiral galaxy M33 pinwheeling silently across Triangulum? Do you want to swim in the flood of Milky Way stars that rise like a silent cloud of steam from the Teapot spout of Sagittarius in the summer? If this kind of observing is your cup of tea, then the wide field of large aperture astronomical binoculars may well be all that you need.

Perhaps the Moon and planets fascinate you? Are you drawn like a moth to a flame by the multi-ringed disk of Saturn's rings; by the ever-changing dance of Jupiter's moons; by the planet-wide dust storms of Mars; and by the mountains, valleys, and craters of our own Moon? If so, a refractor may be the scope for you.

Does your heart beat faster when you think of names like the Pleiades, the Lagoon, the Rosette, the Ring? Do you fall asleep counting NGC objects instead of sheep? Do you want to see, with your own eyes, lights and sights from the distant edges of our Universe? Then a reflector may be the proper instrument to unveil infinity for you.

But perhaps you want to do it all – gather buckets of light for deep space observing, revel in high magnification lunar and planetary views, photograph near and far space in great detail – and still do it with a telescope you can virtually pick up with one hand. If you want it all, then a catadioptric telescope may be the instrument to give it all to you.

The first "P" to juggle, then, is the "P" of Performance. Based on what you want to observe, the chart below can give you a feel for what you can see with the various sizes and types of telescopes, and will start to narrow your search for the right telescope to a few specific types and sizes.

sunspots (with an appropriate solar filter); the phases of Venus; lunar craters as small as four or five miles in diameter; several cloud belts on Jupiter, plus the four Galilean moons; the rings of Saturn (and occasionally a glimpse of Cassini's division, with good seeing); Uranus and Neptune visible as small greenish points

double stars separated by as little as 2 arc seconds in good seeing; faint stars down to magnitude 11.5

the larger globular star clusters, some of the brighter nebulas, virtually all of the Messier objects from a dark sky site (although with relatively little detail visible in many of them)

80mm to 90mm refractor, or 4" to 4.5" reflector, or 3.5" to 5" catadioptric,at powers of 16x to 250x

structure in sunspots (with an appropriate solar filter); the phases of Mercury; lunar rilles and craters less than three miles across; Martian polar caps and major dark surface features during oppositions; several additional cloud belts on Jupiter, with some detail in the belts, plus the shadows of Jupiter's moons on the planet during transits; Cassini's division in Saturn's rings on a regular basis, plus four or five of its moons; Uranus and Neptune visible as very small discs

double stars separated by 1.5 arc seconds or less in good seeing; faint stars to better than magnitude 12

dozens of globular clusters, emission nebulas, planetary nebulas, and galaxies; all of the Messier objects and many of the brighter NGC objects from a dark sky site (with some internal detail visible in many nebulas, although most galaxies will remain relatively featureless hazy patches)

4" to 5" refractor, or 6" reflector,at powers of 30x to 300x

domes, rilles, and other lunar features less than two miles across; more dark surface features on Mars, often during less-than-favorable oppositions; festoons, streamers, and more detail in Jupiter's cloud belts with good seeing; subtle cloud belts on Saturn's disk; many faint comets and brighter asteroids

double stars separated by about 1 arc second in very good seeing; faint stars down to magnitude 13 or better

hundreds of star clusters, nebulas, and galaxies (with hints of spiral structure visible in some galaxies); many, many NGC and IC objects from a dark sky site (considerable detail in nebulas and clusters)

6" refractor, or 8" reflector, or 7" to 9.25" catadioptric,at powers of 50x to 400x

lunar features under one mile across; large clouds and dust storms on Mars; as many as six or seven of Saturn's moons; Jupiter's four Galilean moons start to show as tiny (albeit featureless) discs at high powers; many dimmer asteroids become visible as faint star-like points; seeing conditions start to limit how much solar system detail you can see on an average night

double stars separated by less than 1 arc second in very good seeing; faint stars down to magnitude 14

some globular clusters resolved almost to the core, much internal detail in nebulas and some visible structure in many galaxies from a dark sky site

10" or larger reflector or catadioptric,at powers of 60x to 500x

during infrequent excellent seeing conditions, lunar features to much less than one mile across; small clouds and significant surface detail on Mars, with moons Deimos and Phobos a rare possibility; a wealth of detail in Jupiter's clouds and belts; Enke's division in Saturn's rings often visible; Neptune's moon Triton visible; Pluto visible as faint star-like point; the amount of solar system detail visible will usually be limited by the seeing conditions with large scopes like these, making them less than ideal for regular solar system observing, despite their high resolving power

double stars separated by as little as 0.5 arc seconds in excellent (and accordingly very rare)seeing conditions; faint stars down to magnitude 14.5 and below

thousands of globular clusters, nebulas, and galaxies – virtually all NGC and IC catalog objects – with many showing details invisible in smaller telescopes; faint color visible in some of the brighter nebulas from a dark sky site; it is in viewing these faint objects at low to medium powers that large scopes such as these excel